Myometrium plasma membrane

Young In the myometrium, the Ca2+ waves are from the deep cytoplasmic Ca2+ to the plasma membrane. The intracellular Ca2+ waves should be considered separately from either phasic or tonic smooth muscle types. The myometrium is phasic smooth muscle. And intercellular Ca2+ waves are an entirely different phenomenon altogether. 

These messengers also play a role in regulating contraction of myometrium, which consists of smooth muscle fibres. Contraction is controlled by increases in the concentration of cytosolic Ca ions. Prostaglandins activate Ca ion channels in the plasma membrane of the fibres oxytocin activates release of Ca from intracellular stores. The increase in concentration of Ca ions leads to activation of myosin light-chain kinase which leads to crossbridge cycling and contraction (as described in Chapter 22 Figure 22.12). 

The role of Arf in the in vivo activation of PLD remains unclear for Arfs 1-5, but there is more evidence for Arf6. Whereas Arfs 1-3 are associated with the Golgi, the subcellular distribution of Arfs 4 and 5 is unclear. In contrast, Arf6 is predominantly associated with the plasma membrane where it cycles between this membrane and the cytosol and a vesicular compartment as a function of its GTP/ GDP binding [105-109]. Stimulation of chromaffin cells induces translocation of Arf6 to the plasma membrane and an associated increase in PLD activity [109]. In addition, treatment of the cells with a myristoylated peptide corresponding to the N-terminal sequence of Arf6 inhibits PLD activation [109]. Similar results have been obtained wifh this peptide in myometrium [110]. 

Figure 2. Scheme for isolation of purified plasma membrane fractions from longitudinal muscle of myometrium from estrogenized rats. Variations of the basic approach are used in various smooth muscles. 

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